The present application relates to the technical field of pretensioners for causing a seat belt to increase an occupant restraint force by rotating the spool of a seat belt retractor using reactive gas in the direction in which the seat belt is taken up at the onset of an emergency such as a vehicle crash, the technical field of pretensioners for taking up the seat belt, and the technical field of seat belt apparatuses in a vehicle.
Various types of seat belt retractors provided with a pretensioner have hitherto been devised for use in a seat belt apparatus provided on a vehicle such as an automobile. At the onset of an emergency, such as a vehicle crash, in which a deceleration greater than a usual deceleration acts on a vehicle, such a pretensioner triggers a gas generator for producing reactive gas which in turns rotates the spool of the seat belt retractor in the take-up direction of the seat belt, thereby causing the spool to take up the seat belt. This removes slack from the seat belt in a prompt manner as well as provides the seat belt with a tension, thereby increasing an occupant restraint force.
As one example of conventional pretensioners, a pretensioner is known, which has a piston for producing a force upon receiving gas pressure caused by reactive gas and a plurality of force transmission components, each including a ball, for transmitting such a force produced by the piston to the belt take-up shaft of a seat belt retractor (see, for example, Japanese Unexamined Patent Application Publication No. 2001-63519 and Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2002503168 (both incorporated by reference herein).
FIG. 4 is a diagram schematically showing part of one example of the pretensioner described in JP 2001-63519. FIG. 5(a) is a diagram schematically showing part of FIG. 4. In these figures, reference symbol a denotes a pretensioner (PT), b denotes a pipe having an opening at one end b1 thereof, c denotes a plurality of force transmission components arranged so as to be movable inside the pipe b and in contact with one another, each of which includes a ball made of metal such as steel or aluminum, d denotes a piston including a ball made of a material having sealing properties such as a silicon rubber or a resin, e denotes a tubular pressure container connected to the base end section b2 of the pipe b, f denotes a gas generator housed in the pressure container e, g denotes a ring gear movable into the pipe b through a cutout section b3 located at the end of the pipe b, h denotes levers protruding from the outer circumferential surface of the ring gear g, i denotes internal teeth formed on the inner circumferential surface of the ring gear g, j denotes a spool for taking up the belt in a seat belt retractor, k denotes a pinion secured to the outer circumference of the spool j, m denotes external teeth formed on the outer circumferential surface of the pinion k, n denotes a case provided at the end b1 of the pipe b for housing the force transmission components c ejected from the pipe b, o denotes a gear holder that maintains the ring gear g at a fixed position that does not allow the internal teeth i to be engaged with the external teeth m of the pinion k, and p and q denote a pair of pins provided at the gear holder o for holding the lever therebetween.
The ring gear g is normally held by the gear holder at the fixed position shown in the figures. When the ring gear g is located at this position, the internal teeth i of the ring gear g are not engaged with the external teeth m of the pinion k, which allows the spool j of the seat belt retractor to freely turn in either the seat belt winding direction or the seat belt unwinding direction. The first lever h enters the pipe b through the cutout section b3 while being in contact with the first force transmission component c.
In the event of the aforementioned emergency, the gas generator f is triggered to produce reactive gas. Gas pressure resulting from such reactive gas acts on the piston d, which in turn exerts a pressing force on the force transmission components c. Accordingly, force produced by the piston d is transmitted to the lever h via the force transmission components c. Then, a pressing force is exerted on the lever h, causing the ring gear g to turn counterclockwise while moving to the right in FIG. 4. This causes the internal teeth i of the ring gear g to become engaged with the external teeth m of the pinion k, thereby transmitting rotation of the ring gear g to the pinion k in order to allow the pinion k to rotate counterclockwise, which in turn causes the spool j of the seat belt retractor to rotate in the same direction, namely, in the seat belt take-up direction. Consequently, the seat belt is taken up, which removes slack from the seat belt, thereby allowing the seat belt to increase an occupant restraint force.
FIG. 5(b) is a schematic diagram similar to FIG. 5(a), which shows part of one example of the pretensioner described in JP 2002-503168. As shown in FIG. 5(b), the pretensioner described in JP 2002-503168 employs a cylindrically-shaped piston, instead of a ball-shaped piston. The pretensioner described in JP 2002-503168 also performs nearly the same operation as the pretensioner described in JP 2001-63519.
As shown in FIG. 5(a), the pretensioner a described in JP 2001-63519 has a piston d consisting of a ball, whose shape results in a relatively large gap r between the piston d and a force transmission component c being in contact with the piston d as well as causes the piston d to be relatively difficult to deform so as to come into close contact with the inner wall b4 of the pipe b when the piston d becomes activated to exert a pressing force on the force transmission component c. For this reason, the piston d suffers from an unsatisfactory sealing performance, which causes reactive gas generated by the gas generator f to lose gas pressure, raising concerns that gas pressure resulting from reactive gas is not effectively transmitted to the force transmission component c.
As shown in FIG. 5(b), the cylindrically-shaped piston d described in JP 2002-503168 also has the same reactive gas pressure loss as the pretensioner a described in the aforementioned JP 2001-63519.